On the Instant Pot press on SAUTE twice to choose the MEDIUM setting, and heat olive oil. The screen will show the HOT message. Add the marinated lamb shanks holding from the bone and meat side down to sear. Then start moving them around until browned from all sides. If you feel like your pot is overcrowded, work in batches with more oil.
Transfer the shanks to a plate, tent with foil to keep warm and set aside.
Saute the onion, carrot, and celery, chili if using, and garlic until softened for 5-7 minutes while stirring regularly. Add red wine and let it cook down for a bit (on SAUTE mode).
Put the shanks back in the pot. Add a cinnamon stick, the fresh herbs, and the bay leaves.
Add the leftover marinade if anything is left in the bowl, followed by the chicken broth. Make sure that you add the stock to the side so that it doesn't wash away the seasonings from the meat.
Secure the lid and set the vent to SEALING. Select the PRESSURE COOK/MANUAL setting and set the cooking time for 60 minutes at high pressure. The Instant Pot will take around 10-15 minutes to come to pressure and start cooking. When the cooking program ends, allow the steam to release naturally.
Carefully remove the lid, and transfer the shanks onto a plate; tent to keep warm.